Thermoplastic copolyester elastomers such as segmented copolyester ether have been known heretofore in U.S. Pat. Nos. 3,651,014 and 3,766,146. Those copolyester elastomers are composed of hard segments, consisting of butylene terephthalate chain, and soft segments consisting of poly tetramethyleneoxide glycol chain. The segmented copolyester ether resins have such a good processability and thermal stability at a molding temperature and a short cycle of molding in comparison with other thermoplastic elastomers such as styrene-butadiene-styrene block copolymer and polyurethane. They also have insensitivity to moisture and good elasticity at low temperatures. The segmented copolyester ether, however, have defects in respect to thermal stability and weatherability because of the presence of a polyether segment in the polymer main chain which is essentially poor in thermal stability and weatherability.
Thus, the object of the present invention is to provide thermoplastic polyester elastomer improved in thermal stability and weatherability.
We now have found that the butylene terephthalate-butylene phthalate copolyester has a remarkable elastomeric property.